Method of and means for controlling high frequency voltage in magnetic recorder heads



June 13, 1944. c s 2,351,010

METHOD OF AND MEANS FOR CONTROLLING HIGH FREQUENCY VOLTAGE IN MAGNETICRECORDER HEADS Filed D90. 26, 1942 UUU 36 vuuu Mam av awe s.

UNITED STATES PATENT OFFICE METHOD OF AND MEANS FOR CONTROL LING menFREQUENCY voL'rAGE IN MAGNETIC RECORDER nEAns Marvin Camras, Chicago,111., assignor to Armour Research Foundation, Chicago, 111., acorporation of Illinois Application December 26, 1942, Serial No.470,207

11 Claims. (Cl. 179-1002) This invention relates to improvements in amethod of and means for controlling the high frequency voltage in amagnetic recorder head, and the invention being highly desirable for useprovision of a method ofand means for adjusting the voltage applied to arecording head in a magnetic recording device in a manner to compensatefor variations in characteristics of the recording head, orcharacteristic variations caused by change in speed, or all of them, toacquire optimum efliciency in operation.

A further object of the invention resides in the provision of a simplemethod of and simple in connection with the electrical circuit of ameans for adjusting or varying the voltage apmagnetic recording device,although the invenplied to a recording head in a magnetic recording tionmay have other uses and purposes as will be device over a considerablywide rangeto select apparent to one skilled in the art. the voltage" foroptimum operation and efflciency. In magnetic recording devices whereina sound Frequently a magnetic recording device also recording is madeupon an elongated paramagincludes what may be termed an erasing head sonetic recording medium, such as a metallic tape that the device mayrecord satisfactorily upon or vlvire. a recording hezzidz its frequentlyuised1 to f. recorging mediurrci1 carrying a tpievioilils rgcordapp ysuccess ve magne a ions varying n nng, an as theme ium passes oug t edetensity in keeping with the sound being recorded vice the previousrecording is removed by deto a traveling recording medium such as a tapemagnetization of the recording medium prior to 3: wiradig'helalre areveg-1:21pm in chargchteritsticg thghmggnetizing of the medium inaccordance recor g ea so f one recor g ea wi t e new recording. issubstituted for another in a particular device, This invention also hasfor an object the proan adjustment is desirable to vary the highfrevision of a combination erasing head and control quency voltageapplied to the substitute record- 0 for the voltage applied to therecording head. ing d in der t0 q e Optimum efliciency The inventionalso embodies the feature of by compensating for the variations incharacterproviding a method of and means for adjusting istics of thathead in comparison with the one th ltia applied t a, recording head ofa, Pr vi y ed- Like S l r adjustments magnetic recording device andutilizing the adof the applied voltage are desirable in the event 10justment means to perform an additi l fun a recording medium of adiiferent paramagnetic Om alloy or metal is substituted for thatpreviously still a f th object of the invention is the used- Further ifthe speed of the device 15 provision of a new and 'novel electricalcircuit for changed' that the speed of travel of the inclusion in amagnetic recording device, the circording medium during a recordingoperation, a cu; involving both a recording head and an simlaraigustnienf tzfi t g g g g eimclency erasing head, and being so arrangedthat a simple 5 1 t t s 1 ti i n most variation in the impedance of theerasing head cases 0 e 80 var on o e g requency effects a control overthe applied voltage to the voltage to the recording head when a magneticrecording head recording device is first manufactured so as tocompensate for the relative effect of the record'- a 3 355 2 ifif gfi fgfi a gg g 33223: ing head, medium and speed characteristics.

with the foregoing in mind it is an important recording device, in whichthe recording head is object of this invention to provide a method ofinductively to F source of frequency ltage and t e varia ion in a num erof turns and means for ad usting the high frequency 40 v0 voltageapplied to the recording head of a magof salient part of g z i 2. ignetic recording device in order to acquire opti- 2 232 ig z g g ggg gs gmum eflicienc It is also anyobject of this invention to provideacteristics and advantages of the instant inven- 8 method of and meansfo adjusting the high tion have been above pointed out, others willbefrequency voltage applied to a recording head in come fi f' from thefollowing disclomes' a magnetic recording device, as compared to thetaken In conllmction h the o p ym maximum amplitude of the sound wavesbeing gg g. 1 g i lifi d h t d recorded, esmge gure s asimp e sc ema 1cra- Also a feature of the invention resides in the 0 gram ShowingSalient Parts Of the electrical cuit embodied in the magnetic recordingdevice, including means embodying principles of the present invention,and means by which the method embodied in the instant invention may bepracticed.

' and 9 of opposite polarity,

,As shown on the drawing: "In the illustrated embodiment of thisinvention there is shown a very simplified circuit and apparatusarrangement for a magnetic recording device. Many parts of the recordingdevice and various other circuit connections which may be included inthe device as commercially manufactured are omitted, because the instantinvention particularly centers itself in the recording circuit andimmediately associated apparatus.

It will be appreciated that in a diagrammaticshowing of this charactercertain of. the parts are illustrated in both diagrammatic and explodedfashion for the purpose of clarity, al-

' though these parts will present a different appearance in actualmanufacture.

The salient portion of the apparatus of a magnetic recording devicewhich I have selected for illustration includes a recording headgenerally indicated by numeral 5. This recording head may include a core6, preferably laminated, which is of substantially rectangular shapewith the exception of a rather minute air gap 1, and immediatelyadjacent this air gap 1 the core is shaped to provide confronting polefaces 8 the shaping being such as to reduce the size of the pole facesand concentrate the magnetic flux within a rather small area. Around aleg of the core 6 a coil I is wound to energize the core, and this coil,which itself is energized by the output of an oscillatory circuit, setsup a magnetic field within the core 6 which varies in intensity inaccordance with variations in the sounds being recorded.

The recording medium, in the illustrated instance, is shown as a flneround wire" H, such a wire being approximately the size of a human hair,.004 -to .005 inch in diameter being a satisfactory size. The recordingmedium is usually wound from one reel or spool to the other, and duringthe course of its travel it passes over.or through a groove in the upperface of the recording head. Small increments of the traveling wirebecome successively magnetized in the region of the air gap 1 as thewire travels along, and these'successive magnetizations will vary inaccordance with variations in the sound being recorded.

Frequently, a previously made recording is no longer needed or wanted,and so it is desirable to re-use the medium containing that recordingand place a new recording upon the medium. To expedite matters and savelabor, device may be equipped with a demagnetizing head l2 which is inthe form of a coil through which or adjacent to which the mediiun Htravels'. This coil effectively demagnetizes the medium prior to themedium reaching the record ing head 5 for magnetization in accordancewith the new recording. Thus, an extra and separate operation ofdemagnetizing the recording medium is unnecessary, but a magnetizedmedium maybe placed into the recording device and used as though it.were not ever magnetized, because the erasing head i2 removes themagnetization'from the medium before the new recording is made upon it.

In the case of the instant more fully later appear herein, it is thatcoil or erasing head H which controls the applied voltage to themagnetizing coil l0 and by which that supplied voltage may be varied oradjusted until optimum operating conditions are reached. Both themagnetizing coil l0 and the $1351 8 the recording matically. The

head I2 are energized inductively from an oscillatory circuit which isillustrated in very siniplifled form in the lower portion of thedrawing. This oscillatory circuit includes an oscillator .tube l3, shownin the form of a triode, which has its cathode it connected through aconductor It to a ground it. The plate H of the tube I3 is connectedthrough a conductor I8 to one end of an inductance i9 in the form of ahigh frequency oscillating coil. An intermediate tap is taken from theinductance is by way of a conductor which is connected to a positiveline wire 21. A negativeline wire 22 may be connected through aconductor 23 to the grounded conductor l5 from the cathode of the tube.The two line wires 21 and 22 may be associated with any suitable sourceof current, such, for example, as a battery, and a condenser 24 ispreferably connected across the line wires to bypass alternatingcurrent.

The opposite end of the inductance I9 is connectedthrough a feed-backconductor 25 to the grid 28 of the tube l3. 5 condenser 21 is connectedbetween the conductors I8 and 25 in parallel with the inductance l9 toprovide a tuned circuit for the oscillator arrangement.

As will be apparent to one skilled in the art, the alternating componentof the plate current passing through the inductance I! will set up anoscillating current of high frequency inthe oscillating circuit, and agrid blocking condenser 28 is included in the conductor 25 to keep thehigh positive voltage oil the grid of the tube. A grid biasingresistance 18 is connected across the grid between the conductors 23 and25.

A coil 30 is inductively coupled with the oscillating coil l8, andopposite ends of the coil 33 are connected with opposite ends of theerasing head coil I! by conductors 3| and 32. This coil 30 is sooriented in respect to the oscillating coil I! that the induced field incoil 30 will buciirthe field set up in the oscillating coil l9. Byvirtue of the inductive coupling of the coil 30 with the oscillatingcoll, alternating current will pass through the erasing head coil l2 andthus cause this coil to demagnetize the recording medium passingtherethrough or thereadiacent.

The recording circuit also includes a coil 33 which is inductivelycoupled with both the aforesaid coil 30 and the oscillatin coil is. Oneend of the coil 33 is connected through-a conductor 34 to one end of themagnetizing coil i0 associatedwith the recording head 5. The other endof the coil 33 is connected through a conductor 35 to an amplifyingarrangement generally indicated by numeral 36 and shown onlydiagramother end of the magnetizing coil I 0 is also connected to theamplifying arrangement 36 through a conductor 31. The amplifyingarrangement 36 is connected by way of conductors 38 and 39 to amicrophone or other equivalent pick-up device In which functionsinvention, as will as a pick-up for the sound tobe recorded on the wirell. a

.In view of the fact that high frequency current will be passing throughthe recording circuit, a'condenser M is connected across the conductors35 and 31 leading to the amplifying arrangement, which condenser is ofsuch capacity as to pass high frequency current but act as an insulatorfor low frequency current in order to keep the high frequency currentout of the amplifying arrangement 36.

While the three inductively coupled coils 33, 30 and the oscillatingcoil ii are illustrated in aligned spaced relationship for the purposeof clarity, it will be appreciated that in actual manufacture thesethree coils would be wound in superposed relationship about the sameaxis, or assembled in that relationship in most cases for the purpose ofconvenience and conservation of space. The coils would, of course, beinsulated one from the other, and the coil 30 would be disposed betweenthe oscillating coil l9 and the coil 33 in the-recording circuit.

With the circuit arrangement above described, it. will be appreciatedthat the energization of the magnetizing coil I is controlled by theinductively coupled coil 33. The voltage induced in the coil 33 willresult from a summation of the fields in the opposing coils 30 and IS,the coil 33 not being oriented with respect to the oscillating coil IS.

The voltage induced in the coil 33 will cause a high frequencyalternating current to pass through the magnetizing coil I0 and thusenergize the recording head so that it will successively magnetize'increments of the recording medium H. The low frequency current from themicrophone hook-up will add to the high frequency current and causevariations in the ma netic fields set up by the magnetizing coil in inthe recording head 5 in accordance with variations of sound picked up bythe microphone or equivalent device 40, and thus whatever sound ispicked up by the microphone 40 will be recorded with fidelity on thewire I I.

Now, to illustrate the operation of the instant invention, let it beassumed that the magnetic recording device has just been manufactured.or let it be assumed that some change has been made in a recordingdevice previously used. Such change. by way of illustrative example,could be made by increasing the speed of travel of the recording medium,by the substitution of a new recording head for the one already in use,or by the use of a recording medium of a differentparamagnetic metal orparamagnetic alloy than the medium previously used. Any such changewould set up a variation in characteristics which might tend to detractfrom the optimum performance of the recording device.

The recording device may be brought back into optimum operation, or ifit is a newly manufactured device may be placed into condition foroptimum operation, by varying the high frequency voltage on themagnetizing coil ID. This voltage may be varied by increasing ordecreasing the number of turns in the erasing head coil IL From thecircuit above set forth, it will be apparent that if the number of turnsin the erasing head coil I2 is reduced, there will be more current flowin the coil 30, and consequently since this coil is in opposition to theoscillating coil I9, there will be less voltage induced and less currentflow in the coil 33 and likewise in the magnetizing coil iii. If thenumber of turns in the erasing head coil i2 is increased, an oppositeresult will follow. Thus, it will be seen that a simple, economical andfacile adjustment of the erasing head coil. or of the coil 12 in someother location in the event it is not used as an erasing head, willexpeditiously place the recording device in condition for optimumoperation when the device is newly built, or when some change has beenmade in the devic causing a variation in characteristics of somecomponent part of the magnetizing circuit. It will be noted thatchanging the number of turns in the coil l2 will vary the high frequencyvoltage on the magnetizing coil l6 over a considerably wide range.

From the foregoing, it is apparent that I have provided a novel methodof and means for adjusting the high irequncy voltage impressed on themagnetizing head of a magnetic recording device. in order to make therecording device function at optimum efficiency. It will be noted thatthe adjustment may be made simply and with great ease and compensate forvariances in characteristics of component parts of the circuitconnections and apparatus. be noted that if an erasing head is utilizedin the particular magnetic recorder, that erasing head may be made togovern the voltage impressed upon the magnetizing head and be used tovary that impressed voltage, as ell as perform its own function ofdemagnetizing the recording medium, this providin a compact wiringarrangement, adding to the economy of production and use, andeliminating the need of a separate controlled circuit.

It will. of course. be understood that various details of constructionmay be varied through a .wide range without departing from theprinciples of this invention and it is, therefore, not the purpose tolimit the patent granted hereon otherwise than necessitated by the scopeof the appended claims.

I claim as my invention:

1. In a magnetic recording device, an oscillatory circuit, a buckingcircuit, a magnetizing circuit, each of said circuits embodying a coil.

and said coils being inductively coupled with the coil of the buckingcircuit between the coils of the oscillatory and magnetizingcircuits,the coil of the bucking circuit being oriented to oppose the coil of theoscillatory circuit, and the coil of the magnetizing circuit not beingoriented with respect to the oscillatory circuit coil so the magnetizingcircuit coil receives an induced voltage which is a result of thesummation of the fields of the other two coils.

2. In a magnetic recording device, an oscillatory circuit, abucking-circuit, a magnetizing circuit, all said circuits beinginductively coupled, and means in the bucking circuit by which theimpedance of the bucking circuit may be varied to adjust the inducedvoltage of the magnetizing circuit,

3. In a magnetic recording device, an oscillatory circuit, a buckingcircuit, a magnetizing circuit, including a recording head'to magnetizea traveling recording medium, all said circuits being inductivelycoupled, means'in the bucking circuit by which the impedance of thatcircuit may be varied to control the voltage induced in the magnetizingcircuit, and said means being positioned to demagnetize the recordingmedium before it reaches said magnetizing head.

4. In a magnetic recording device, a magnetizing circuit, including arecording head to magnetize a traveling recording medium, and electricalmeans associated with said circuit by which the voltage in said circuitmay be varied, said means also functioning as an erasing element todemagnetize the recording medium prior to its being acted upon by saidrecording head.

5. In a magnetic recording device, an oscillatory circuit, a buckingcircuit, a magnetizing circuit, each of said circuits embodying a coil,said coils being inductively coupled so that the bucking and magnetizingcircuits receive energization inductively from the oscillating circuit,

Further, it will latory circuit, a bucking circuit, a magnetizingcircuit, all said circuits being inductively coupled, said buckingcircuit being in opposition to said oscillatory circuit, and animpedance in said bucking circuit which may be varied to control thevoltage induced in said magnetizing circuit.

7. In a magnetic recording device, an oscillatory circuit, a buckingcircuit, a magnetizing circuit including a recording head to magnetize atraveling recording medium, all said circuits being inductively coupled,and a coil providing an impedance in said bucking circuit and which byvarying the number of turns therein may be used to control the voltageinduced in said magnetizing circuit, said coil being positioned adjacentthe path of the recording medium to also function as an erasing elementand demagnetize the medium prior to the action of said recording head.

8. The method-oi adjusting the voltage applied to the recording head 'ofa magnetic recording device wherein a magnetizing circuit, an

oscillating circuit, and a bucking circuit are inductively coupled,which consists in varying the impedance in the bucking circuit.

9. The method of controlling the voltage applied to the recording headin a magnetic recording device wherein a magnetizing circuit isinductively coupled with an oscillating circuit, which includes thesteps of setting up an opposing fleld to that oi the oscillating circuitin a manner that the magnetizing circuit receives a voltage resultingfrom a summation of the magneticneld of the oscillating circuit and theopposing field.

10. The method of controlling the voltage applied to the recording headin a magnetic recording device wherein a magnetizing circuit isinductively coupled with an oscillating circuit, which includes thesteps of setting up an opposing field to that of the oscillating circuitby inductively coupling an impedance circuit between the couplings ofthe magnetizing and oscillating circuits, and varying the impedance intheimpedance circuit.

11. The method of controlling the voltage ap plied to the recording headin a magnetic recording device wherein a. magnetizing circuit isinductively coupled with an oscillating circuit, which includes thesteps 01' setting up an opposing field to that of the oscillatingcircuit by inductively coupling a bucking circuit having an impedancecoil between the couplings of the magnetizing and oscillating circuits,and changing the number of turns in the impedance coil.

'MARvm CAMRAB.

